Electric furnace.



C. A. PFANSTlI-LHL.

ELECTRIC FURNACE.

n APPLICATION FILED APR. l5, 1915. 1,218,582. Patented Mar. 6, 1917.

.0 w 10W@ 6 MiN w PATENT onirica CARL A. PFANS'IIEHL,

NORTH CHICAGO, ILLINOIS,

OF WAUKEGAN, ILLINOIS, ASSIGNOR TO PFANSTIEHL COMPANY,

A CORPORATION OF DELAWARE.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Mar. 6, 1917.

Application filed April 15, 1915. Serial No. 21,559.l

To all whom t may concer/n.'

Be it known that I, CARL A. PFANsTrEr-IL, a citizen of the United States, residing at Waukegan, in the county of Lake and'State of Illinois, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a full, clear concise, and exact description, reference ring had to the accompanying drawings, forming a part of this specification.

My invention relates to electric furnaces. One of the particular objects of my present invention is to provide an efficient and economical apparatus for use in reducing the oxids of tungsten to the metal. In accompli Shing the ob 'ects of my invention I utilize a refractory tube, or cylinder, provided with a gas tight jacket or glaze to prevent the escape of hydrogen which, as Will be presently explained, is passed through the refractory tube during the heating operation. The refractory tube, which is preferably of alundum, is conveniently supported in a` metallic box which contains silica sand or other refractory material surrounding the alundum tube. In the embodiment of my invention subsequently described and claimed the electrical heating element employed is a resistance Wire of relatively large crosssection composed of an alloy of nickel and chromium, disposed and suitably retained in the interior of the alundum tube constituting the furnace heating chamber. The resistance wire is coiled against the inner surface of the alundum tube, Which is adapted to receive materials to be treated Within the furnace.

The arrangement and combination of parts is such that the necessity for a heating element of tungsten, platinum, molybdenum or other metal having a relatively high fusing point is avoided. In the past it has been customary to dispose the resistance element about the outside of the refractory chamber, and in order to secure a sufficiently high degree of heat Within the chamber it has been practically necessary to employ heating elements of tungsten, platinum, molybdenum or tantalum, any of which withstands an extremely high temperature. ByA employing a resistance element outside the chamber but heated to a very high temperature, it has been possible to secure lovver, but still suiiiciently hi h temperatures within the chamber. With t e possible exception of platinum, it is practically necessary to Vprotect any of these resistance elements, when Worked at eX- tremely high temperatures, from the oxidizing effect of atmospheric air. Vhen the resistance elements have been Wound or otherwise disposed outside the chamber 'to be heated, it has been the custom to surround the heating element with an outer chamber, practically air tight, and to supply this outer chamber with hydrogen or other inert gas, thereby protecting the heat mg element against oxidization. In many operations, particularly reduction operations, it is necessary to supply hydrogen to the interior of the reduction chamber. It has, therefore, been the custom to employ a reduction chamber formed of more or less porous material, through the walls of which i the hydrogen supplied to the outer chamber Will seep or percolate into the space Within the reduction chamber, the reduction chamber being supplied in this Way with the hydrogen gas necessary to the sat# isfactory reduction of materials Within .the reduction chamber.

a In order that all of the air and other impuritiesv maybe completely expelled from the outer chamber, lwhich .usually is filled With a refractory material in powdered, granular or other porous form, it is necessary to permit hydrogen to flow into the outer chamber and through lthe Walls of the reduction chamberfor a considerable period of time beforethe furnace is in shape for the reduction operation. This complete expulsion of Vlair and other impurities is necessary `in order that the air or other impurities may not percolate into the reduction chamber during the reduction operations. It is not safe in these furnaces of the prior art to'heat the resistance ele ment to the high temperature necessary in operation until all of' the air and other oxidizing agent has been expelled. It is the custom, therefore, to run the furnace for a period of several hours at a low temperature, with hydrogen supplied to the outer chamber, and onlyafter the air and other impurities havebeen expelled is the `temperature raised to the high degree necessary in carrying on the reduction operations.

In the furnace of my invention the reduction chamber is glazed on the outside,

thus preventing the escape of hydrogen which is supplied directly to the interior of the reduction chamber. Since also the resistance Wire or element is inside the reduction chamber, the hydrogen or other gas which is supplied to the reduction chamber primarily for the purpose of carrying on the reduction serves also to protect the resistance element. But very little air is re tained inside the glazed outer surface of the reduction chamber, as a-result Whereotl the hydrogen or gas must be passed through the :furnace for only a few minutes in order to put the tui-nace in shape for the reduction operations.

There is a further decided advantage in laying or winding the resistance element inside the Walls oi the reduction chamber, due to the lower temperature at Which the resistance element may be Worked to produce the required high degree oi temperature Within the reduction chamber.

rlhese and other features oit the furnace of my invention are fully set forth in the following detailed description in Which reterence is made tothe accompanying drawings, in Which- Figure l is a view partly in section and partly in elevation of the improved furnace of my invention; and

Fig. 2 is a fragmentary sectioned View of the modified embodiment of my invention wherein the refractory tube lconstituting the heating chamber is glazed to prevent the escape oit hydrogen.

Similar referencev characteisreter to similar parts throughout the drawings.

Referring first to Fig. 1, at 3 is illustrated a metal boit, or housing, arranged to contain a quantity of silica sand or other refractory material illustrated at ll. lilirtending through the ends of the boX 3 and embedded in the refractory material t. is a steel tube or sleeve" 5 Within which is snugly tted a refractory tube 6, preferably of alundum. vent the escape ot hydrogen which is passed through the heating chamber from end to end, as will be subsequently explained, and also serves to support the alunduin tube in case the same should crack or break, due to sudden heating or other causes.

Disposed Within the aluiidum tube 6 and coiled against the innersurface oit the alundum tube is an electrical heating element 7, :formed of a wire composed of an alloy of nickel and chromium. fis illustrated in the drawings, the convolutions of the heating element are embedded in a suitable re liractory cement 8 composed, for exam le, ottl alumina and a small proportion of all clay, which serves to retain the heating element in position and also serves to present a substantially smooth cylindrical inner surtace to the furnace chamber. rlhe ends of '.lhe stoel tube 5 serves to lpre- :init-inca the heating element are conveniently led to the ends of the alundum tube, as illustrated, and are connected in any suit-able manner with a source ot current capable ot supplying the required amount oit' electric energy. ln the drawings l have illustrated a current source comprising an alternating current generator, regulating rheostat and transformer.

lily locating the heating element Within the alundum tube 6 l am enabled to utilize Nichrome7 or other wire composed substantially of an alloy ot nickel and chromium for the heating element instead oit using tungsten, platinum or tantalum for this purpose. Nichrome Wire is much cheaper' than Wires otl the materials previously mentioned. Moreover by disposing the heatpose oit edecting the necessary chemical re duction. No matter what material may be employed in the heating element, there is, therefore, a large saving in hydrogen or other gas and a large saving in the amount oi' time necessary to put the tui-nace in condition for operation. y

lhe alundum tube'is provided With end closures in the form ot plugs 9 and 10, as illustrated. Passing through the plug 9 is a pipe 11, which is designed to be connected by a'tiexible tube 1Q with a source of hydrogen supply. Passing through the plug 10 is a pipe 13 which extends a considerable distance beyond the outer end of the plug. Bv providing the larrangement last described ll am enabled to pass hydrogen through the heating chamber. troni end to end during the reduction operation.- 'lhe hydrogen passing through the pipe 13 is preferably burned at the end of the pipe as it escapes.

A, thermal couple 14C is located in close proximity with the outside of. the' reduction chamber, as indicated in the drawing, and is connected by suitable Wires with an electric pyrometer indicated at 15. The thermal couple is not, oli course, heated fully to the temperature within the reduction chamber, but experience or preliminary test will enable the operator to know What temperature must be indicated by the pyrometer in order to secure the necessary degree ot heat Within the reduction chamber.

lf the furnace is to be operated at an eX- tremely high temperature, it may be found desirable to incase the end of the thermal couple in a plug or block of graphite indicated at 16, one end of the plug or block of graphite resting directly upon the outer Wall of the reduction chamber. Ordinarily it is notnecessary to use this graphite plug or block when the outer shell of the reduction chamber is formed of steel, as indicated in Fig. 1, because the thermal couple will easily withstand any temperature which the steel shell will withstand. 'I have found it desirable, however, to employ the graphite, plug or block when the furnace is worked at extremely high temperatures, in which case the steel shell for the reduction chamber will be dispensed with.

In utilizing the herein-described furnace for reducing tungsten trioxid to metallic tungsten small quantities of the trioXid are placed in nickel, porcelain or alundum boats which are placed within the heating chamber of the reducing furnace and within the heating coil 7. The tungsten trioXid is -heated about two hours at a temperature of 600 degrees centigrade, after which the temperature is increased ap- ]roximately to '1100 degrees centigrade.

uring the heating operation hydrogen is passed through the'tube from end to end to effect the reduction of tungsten trioxid to vary fine particles of metallic tungsten.

In Fig. 2 modified form of the reducing furnace comprising an alundum tube 20 constituting a reduction chamber and within the alundum tube 20 is a heating element generally similar to the heating element illustrated in Fig. 1 and described in connection therewith. It will be noted that the alundum tube 20 is not provided with a steel sheath as is the alundum tube illustrated in Fig-1. In the embodiment tube is glazed upon the outside to prevent the escape of hydrogen from the reduction chamber. The alundum tube 20 is embedded in silica sand or other refractory material 22 as illustrated. v

.This form of furnace would be employed operations requiring extremely high temthe steel sheath would not peratures which withstand, and it would be principally with this modification 'that the carbon block 16 would be used in connection with the ther-v 1914. the furmal couple illustratedl in. Fig. 1.

Before hydrogen is 'admitted to nace heating chamber as reviouslydescribed, it is thoroughly purified by one vof the processes commonly employed by persons I have illustrated a somewhat shown in Fig. 2 the alundum v skilled in the art to which my invention appertains. I do not deem it necessary to illustrate or describe in the present application the apparatus or process whereby commercialhydrogen is purified to adapt it for use in my improved furnace. Y

.Having now fully described my invention, what I claim as new anddesire to secure by Letters Patent of the United States is:

1. An electric furnace comprising, in combination, a hollow cylindrical tube of alun- `dum having a gas-tight outer sheath, an

electric current conducting wire helically coiled within said tube from end to end and substantially in contact with the inner walls of the tube, a refractory cement filling the interstices between the several convolutions of the said wire and presentin a Smooth cylindrical inner surface, plugs o refractory material substantially filling the open ends of the tube, and piping for conveying a supply of hydrogen directly to and from the interior of .said tube.

2. An electric furnace comprising, in combination, a hollow cylindrical tube of alundum having its outer surface provided with a glaze impervious to air or gas, anelectric current conducting coiled within said tube from end to end and substantially in contact with the inner walls of the tube, a refractory cement filling the interstices between the several yconvolutions of the said wire and presenting a smooth cylindrical inner. surface, plugs of refractory material substantially filling the open rsa wire helically ends of the tube, and piping for conveying a n and means for conveying an inert gas to and from the interior of the chamber.

f In witness whereof, my name this 21st day of November,

I hereunto subscribe A. D.

l CARL A. PFANSTIEHL.

Witnesses:

MARGARET OKEEFE, J. C. BAKER. 

